Linux specifically does not use the GPLv3 for exactly this reason. rms et al. complained about "tivoization", which came from tivo shipping boxes that contained the code but were locked down. Linus didn't really care as much, or at least not enough to re-license. He didn't like the restriction, and new that such a provision would prevent exactly what MS is now doing: allowing more freedom for the users.
That's orthogonal though. WSL would be fine even with GPLv3. It runs on a hypervisor. WSL poses no restrictions on modifying the source of the kernel. You can fork, rebuild and run. You can't on a tivo device.
Not exactly. Microsoft is trying to expand functionality in certain places to allow things like CUDA acceleration, AF_PACKET support, and other important hardware-y things that WSL can't handle. You're right that you can run a different kernel, but Microsoft has modified theirs for WSL. For that reason, they have to release modifications.
Linux specifically does not use the GPLv3 for exactly this reason. rms et al. complained about "tivoization", which came from tivo shipping boxes that contained the code but were locked down. Linus didn't really care as much, or at least not enough to re-license. He didn't like the restriction, and new that such a provision would prevent exactly what MS is now doing: allowing more freedom for the users.